Tangential Knock Outs and 250.97 Compliance

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infinity

infinity

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We recently installed some Heavy Duty 200 amp Eaton non-fused disconnect switches {model DH364UGKN3NP}, the circuit voltage is 480 volts. They contain Tangential KO's which were used with 1.5" EMT leaving a few of the larger KO's intact (KO goes up to 2.5"). The question arose whether or not these Tangential KO's would need a bonding bushing to comply with 250.97. It seems that the KO type, Tangential is not listed in 250.97 and the KO's are specifically listed by the manufacturer as being Tangential. The other question arose as to how to find out if a particular KO is suitable for bonding over 250 volts as outlined in the exception in 250.97.

One other thing, each conduit contains a copper EGC properly terminated on both ends and the circuit originates in a distribution board with field punched 1.5" KO's. Would this make the entire first paragraph of this post moot?

http://www.eaton.com/Eaton/Products...itches/HeavyDuty/Non-Fusible/index.htm#tabs-2

20120921_085251.jpg
 
They are tangential in that all have a common point with one another but that's the first time I ever heard it used in this context,,,is that a common notation for K.O.'s?

dick
 
I have been told that the Tangential knockoutsare not covered by 250.97 as there is direct contact to the enclosure with raceways,
I don't recall the reliability of my source so I sent an inquiry to U.L.

In this situation my opinion is that it is a mute question as your conduit is bonded by the termination at the panelboard and since you have a EGC the conduit is not serving in that capacity.
 
augie47 said:
I have been told that the Tangential knockoutsare not covered by 250.97 as there is direct contact to the enclosure with raceways,
I don't recall the reliability of my source so I sent an inquiry to U.L.

In this situation my opinion is that it is a mute question as your conduit is bonded by the termination at the panelboard and since you have a EGC the conduit is not serving in that capacity.
Click to expand...

The way I see it there are two issues:
#1) are tangential KO's listed for bonding over 250 volts and
#2) if the raceway is bonded by a punched KO on the other end is issue #1) even relevant since the raceway is bonded at one end.
 
Grounding Enclosures - 250 IV
Equipment Grounding - 250 IV

Some others that I try to remember :)

250.96 Bonding other Enclosures

If that doesn't work for you try 250.86.

Your link only goes to Eaton's cover page.

A little off as to your subject but always a good reminder when talking about grounding 250.64(E), 3rd and 4th sentence. A few sub articles have stars in my book for this article!

The eccentrical I always have to re-read this one, I always remember get it wrong... :thumbsup: no comment!
 
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augie47 said:
I have been told that the Tangential knockoutsare not covered by 250.97 as there is direct contact to the enclosure with raceways,
I don't recall the reliability of my source so I sent an inquiry to U.L.

In this situation my opinion is that it is a mute question as your conduit is bonded by the termination at the panelboard and since you have a EGC the conduit is not serving in that capacity.
Click to expand...

Augie,

What code section would you cite to say that this is permitted?

jumper said:
The word "tangential" does not appear in the UL white book.

IAEI says that they are a form of eccentrical.

http://www.iaei.org/magazine/2007/1...-at-over-250-volts-how-about-on-outlet-boxes/
Click to expand...

So according to that Q & A (if still applicable) enclosures with concentric or eccentric KO's are no longer tested or permitted to be used for bonding over 250 volts.
 
infinity said:
The way I see it there are two issues:
#1) are tangential KO's listed for bonding over 250 volts and
#2) if the raceway is bonded by a punched KO on the other end is issue #1) even relevant since the raceway is bonded at one end.
Click to expand...
#1) The article linked by jumper says no (unless manufactured and listed to UL 50 prior to 2005)

#2) 250.97 subject is bonding for electrical continuity. To be electrically continuous requires effective bonding at both terminations. Analogously, would you consider a wire terminated at only one end as electrically continuous?
 
Smart $ said:
#2) 250.97 subject is bonding for electrical continuity. To be electrically continuous requires effective bonding at both terminations. Analogously, would you consider a wire terminated at only one end as electrically continuous?
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The raceway contains an EGC which is properly terminated at both ends. The 1.5" EMT is properly bonded by the EMT connector and 1.5" KO punched on the distribution board. Is anything else required?
 
infinity said:
The raceway contains an EGC which is properly terminated at both ends. The 1.5" EMT is properly bonded by the EMT connector and 1.5" KO punched on the distribution board. Is anything else required?
Click to expand...
Electrical continuity of the raceway (to the enclosures). 250.97 makes no exception for the inclusion of a wire-type EGC in the raceway of concern.
 
I think Smart$ is correct** according to the wording of 250.97
"electrical continuity of metal raceways.....shall be ensured".
I had always looked at it as to the raceway being grounded or not, but I see his point.

**( that sounds better than I was wrong :D )
 
Smart $ said:
Electrical continuity of the raceway (to the enclosures). 250.97 makes no exception for the inclusion of a wire-type EGC in the raceway of concern.
Click to expand...

I'm not so sure that the EGC cannot be used to comply with the continuity requirement. The run could have a piece of NMFC or FMC at the end, neither of which would provide continuity of the raceway.
 
infinity said:
I'm not so sure that the EGC cannot be used to comply with the continuity requirement. The run could have a piece of NMFC or FMC at the end, neither of which would provide continuity of the raceway.
Click to expand...
"Could" being the operative word... and then guess what it would take for the raceway to exhibit electrical continuity...?

Not wanting to be the devil's advocate here, but the requirement says what it says... :huh:
 
Smart $ said:
"Could" being the operative word... and then guess what it would take for the raceway to exhibit electrical continuity...?

Not wanting to be the devil's advocate here, but the requirement says what it says... :huh:
Click to expand...

Not disagreeing with you but then do you agree that you can never have a run of EMT with FMC or NMFC at the end and be compliant with the continuity requirement? This is a pretty common installation practice.
 
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